Here is the full list of all 34 Demonheart achievements.
Finish the game as Good Bright and as Evil Bright.
Kill Mark.
Kiss Ari.
Read the book about demonspawn in Chapter 1.
Finish Chapter 5.
Kiss Sir Brash.
Max out both Evil and Defiant points.
Max out both Evil and Tactful points.
Max out both Good and Defiant points.
Decipher the whole message in Chapter 5.
Finish Chapter 4.
Max out both Good and Tactful points.
Read all the entries of Rivera's journal.
Decipher the message in Chapter 4.
Finish Chapter 3.
Ask the demonspawn as many questions as you can.
Decipher all the messages in Chapter 3.
Finish Chapter 2.
Decipher the message in Chapter 2.
Finish Chapter 1.
Decipher all the messages in Chapter 1.
Examine Mr. Edgardo after the dinner with Orchid.
Molest the demonspawn.